The objective of this study is to evaluate the effects of incorporating bioactive peptides (BPs) from salmon aquaculture by-product into the diets of gilthead seabream (Sparus aurata), focusing on growth performance, blood biochemistry and gut health and their interlink. Furthermore, the investigation explores potential advantages within the climate change context, providing a comprehensive understanding of the diverse implications associated with this dietary approach. For this purpose, three diets with varying BP levels (0%BP0, 5%BP5, 10%BP10) as substitutions for fish meal (FM) were administered to triplicate fish groups over a 58-day trial period. Successively, fish were exposed to suboptimal environmental conditions (high water temperature, low oxygen) for 7 days.
No significant difference between fish fed the three experimental diet was observed for growth performances parameters. The highest dosage of BP (BP10) induced a significant increase of bacterial α-diversity, suggesting a potential benefits. Additionally, samples belonging to the experimental diet groups (BP5 and BP10) seemed less responsive to stressing conditions, in terms of microbiome variations. However, considering the microbiome profiles at T1 only (Fig. 1A), fish fed BP5 and BP10 showed a significant decrease in abundance of Brevibacillus and Bacillus, potentially indicating a reduced fish health. Moreover, challenging environmental conditions combined with high dietary inclusion of BP (10%) triggered an elevated plasma glucose, creatinine and uric acid levels, potentially indicating impairment of kidney function and reduced fish fitness. Furthermore, it was observed that in fish fed BP10, opportunistic fish pathogen as Stenotrophomonas and Acinetobacter increased after environmental stress and this data were positively correlated to higher lactate hematic concentration, suggesting a physiological distress exacerbated by adverse environmental conditions. Overall, while BP inclusion offers a sustainable alternative protein source, incorporating more than 5% in the diet might compromise fish health under challenging environmental conditions.